For many years it has been common practice in the wind turbine industry to protect the leading edge of the blades against erosion resulting from collision with raindrops, dust particles, insects, hailstones and the like by gluing an anti-erosive tape onto the critical areas.
Applying the tape is a difficult and time consuming task which many blade manufacturing companies would prefer to avoid. Furthermore, the edge of the tape may result in unwanted turbulence and noise.
Substituting the tape with a highly anti-erosive topcoat reduces production time and ensures a smooth surface.
Up till now, it was believed that a main feature of coatings for such edges should be a high degree of abrasion resistance, but it has recently been suggested that elasticity also plays a role.
US 2004/110918 A1 discloses a process for producing cross-linkers for polyurethane powder coatings. The cross-linkers typically includes few free isocyanate groups, however uretdione groups will disintegrate upon heating and result in further isocyanate groups. US 2007/0142608 A1 discloses the further developments of the process of D1 in which a bismuth-containing catalyst is used.
WO 2005/092586 A1 discloses methods for preparing wind turbine blades coating with a thermoplastic film, which is suitable as the wind turbine blade surface. Preferably, the materials to form the coating comprise acrylic-based material, polycarbonate, FCDF (polyvinylidene fluoride), polyurethane or a blend.
U.S. Pat. No. 4,859,791 discloses polyols for use in composition for the preparation of polyurethanes. The polyols have a molecular weight of 850-2,000, a functionality of 5-9, and are prepared from polyfunctional polycycloaliphatic or aromatic carboxylic acids and optionally up to about 50% by weight of at least one acyclic, polyfunctional carboxylic acid.
JP 2006-124610 and JP 2006-328252 disclose coating compositions of a combination of a polyol and a polyisocyanate of the allophanate type.
WO 2009/111227 discloses composites comprising a multi-layered coating system, including a topcoat of a functional component comprising hydroxyl and/or amine groups, and a curing agent comprising isocyanate and/or anhydride functional groups.
It has now been found that polyurethane-based coatings formed by a combination of a particularly selected type of polyols and particularly selected types of polyisocyanates constitute excellent outermost coatings for wind turbine blades in that such coatings provide a suitable combination of flexibility and durability.